Two-pore channels as regulators of proliferation in cancer

ABSTRACT

The present invention relates to the discovery that two pore K +  channel (2PK) gene expression is increased in tumors and tumor cell lines, especially prostate tumor cells. The present invention encompasses methods for disease diagnosis, drug screening and the treatment of cancer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority as a divisional applicationto application Ser. No. 12/299,852, filed Nov. 6, 2008 under 35 U.S.C.§121, which is a national phase (371) application of internationalapplication PCT/US2007/011339, filed May 9, 2007 which claims benefit ofpriority to provisional applications, 60/835,336 filed Aug. 2, 2006 and60/799,486 filed May 10, 2006 under 35 U.S.C. §119(e), the entirecontents of which are hereby incorporated by reference as if fully setforth herein.

STATEMENT OF GOVERNMENTAL INTEREST

This invention was made with Government support under Contract No.W81XWH-06-1-0141 awarded by the Department of Defense. The Governmenthas certain rights in the invention.

1. INTRODUCTION

The present invention relates to the discovery that two pore K⁺ channel(2PK) gene expression is increased in tumor cell lines, especiallyprostate tumor cells. The present invention encompasses methods fordisease diagnosis, drug screening and the treatment of cancer.

2. BACKGROUND OF INVENTION

Cancer is a disease marked by the uncontrolled growth of abnormal cells.Cancer cells have overcome the natural controls imposed in normal cells,which have a finite lifespan. As the growth of cancer cells continuesthe cancerous cell may develop a more aggressive growth phenotype. Ifleft untreated, metastasis, the spread of cancer cells to distant areasof the body by way of the lymph system or bloodstream, may ensue,destroying healthy tissue. Carcinoma of the prostate (PCA) is the mostfrequently diagnosed cancer in men in the United States, and is thesecond leading cause of male cancer deaths (Karp et al., 1996, CancerRes. 56:5547-5556).

It would therefore be beneficial to provide methods and reagents for thediagnosis, staging, prognosis, monitoring, and treatment of cancers.

3. SUMMARY OF THE INVENTION

The present invention relates to methods and compositions for modulatingthe activity of the two-pore domain K⁺ channels as a means formodulating the proliferation of cancer cells. Specifically, the presentinvention relates to methods and compositions for modulating theactivity of the TREK-1 two-pore domain K⁺ channels (“TREK-1”) as a meansfor modulating the proliferation of prostate cancer cells. Suchmodulation can be used to reduce or inhibit the proliferation ofprostate tumor cells. The invention is based on the discovery thatTREK-1 is over expressed in human prostate cancer cells as compared tonormal prostate cells, as well as in breast, colon and bladder cancercells. Moreover, inhibition of TREK-1 activity was found to inhibit theproliferation of tumor cells.

The present invention further relates to methods for the diagnosticevaluation and prognosis of cancer, especially prostate cancer. Forexample, TREK-1 nucleic acid molecules can be used as diagnostichybridization probes or as primers for diagnostic PCR analysis fordetection of abnormal levels of expression of the TREK-1 gene.Antibodies to TREK-1 gene product can be used in a diagnostic test todetect the level of TREK-1 gene product in tissue samples. In specificembodiments, measurement of TREK-1 gene product levels can be made todetect or stage cancer, especially prostate cancer.

Still further, the present invention relates to screening assays thatutilize the TREK-1 gene and/or TREK-1 gene product for theidentification of compounds which modulate TREK-1 gene expression and/orthe activity of TREK-1 gene products. In a preferred embodiment of theinvention, the compound is one that is capable of inhibiting theactivity of TREK-1 and effectively reducing or inhibiting theproliferation of cancer cells. Such compounds can be used as agents toprevent and/or treat cancer. Such compounds can also be used to palliatethe symptoms of the disease, and control the metastatic potential of thecancer.

Specifically, the present invention provides a method for identifying acompound that activates TREK-1 activity comprising (i) contacting a cellexpressing TREK-1 with a test compound and measuring the level of TREK-1activity; (ii) in a separate experiment, contacting a cell expressingTREK-1 protein with a vehicle control and measuring the level of TREK-1activity where the conditions are essentially the same as in part (i),and then (iii) comparing the level of TREK-1 activity measured in part(i) with the level of TREK-1 activity in part (ii), wherein an increasedlevel of TREK-1 activity in the presence of the test compound indicatesthat the test compound is a TREK-1 activator.

The invention also provides a method for identifying a compound thatinhibits TREK-1 activity comprising (i) contacting a cell expressingTREK-1 protein with a test compound and measuring the level of TREK-1activity, (ii) in a separate experiment, contacting a cell expressingTREK-1 protein with a vehicle control and measuring the level of TREK-1activity, where the conditions are essentially the same as in part (i)and then (iii) comparing the level of TREK-1 activity measured in part(i) with the level of TREK-1 activity in part (ii), wherein a decreaselevel of TREK-1 activity in the presence of the test compound indicatesthat the test compound is a TREK-1 inhibitor.

In yet another embodiment of the invention, a method for identifying acompound that inhibits proliferation of cells expressing TREK-1 activitycomprising (i) contacting a cell expressing TREK-1 protein with a testcompound and measuring the level of cell proliferation, (ii) in aseparate experiment, contacting a cell expressing TREK-1 protein with avehicle control and measuring the level of cell proliferation, where theconditions are essentially the same as in part (i) and then (iii)comparing the level of cell proliferation measured in part (i) with thelevel of cell proliferation in part (ii), wherein a decrease level ofcell proliferation in the presence of the test compound indicates thatthe test compound is an inhibitor of cell proliferation.

The invention further provides pharmaceutical compositions comprising abiologically active agent that modulates the activity of TREK-1 incombination with a pharmaceutically acceptable carrier.

4. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. TREK-1 is expressed in prostate cancer cell lines but not innormal prostate epithelium. Cell lysates were prepared from LNCaP (lane1), PC-3 (lane 2) and normal prostate epithelial (lane 3) cell culturesand fractionated by SDS-PAGE. The proteins were blotted tonitrocellulose and detected by ECL according to the manufacturer'sinstructions with a polyclonal rabbit anti-TREK-1 primary antibody(Alomone). Beta-actin was measured as a loading control on the sameblots. These results are typical of two experiments.

FIG. 2. PC-3 cells express TREK-1 current which can be “knocked-out” byover-expression of a dominant-negative mutant (dn-TREK). Panel A. TREK-1current is defined as the sipatrigine-sensitive current and is measuredusing a ramp protocol. A series of 800 ms steps from −120 mV to +70 mV(increasing 10 mV each step) from a holding potential of −20 mV areapplied. To eliminate contamination by Na⁺ current a prestep to −90 mV(40 ms) is applied before each step. Sipatrigine (50 μM) is applied bysuperfusion for 3 min while recordings are taken every 30 s. The tracesreported in the figure are the result of the subtraction of the controlcurrent from the current in the presence of sipatrigine at steady state.Panel B. PC-3 cells were co-transfected with dn-TREK and pEGFP-C1plasmids. 48 h later, dn-TREK cells were identified by greenfluorescence and recordings were made as described above. Panel C. Datafrom numerous cells are summarized in the bar graph.

FIG. 3. Dominant-negative TREK-1 reduces proliferation of PC-3 cells.PC-3 cells were transfected with either dn-TREK (or a control vector(pEGFP) using GeneJammer (Stratagene) under standard conditions.Proliferation of these cells was measured using the MTT assay after thecells were plated at 1×10⁵ cells/well in 96 well plates. Data arepresented as the mean±SEM of five experiments. * p<0.05 vs control andEGFP FIG. 4. Normal prostate epithelial cells (NPE) express no TREK-1current but a TREK-1 virus can be used to over-express the channel.Current was measured in cultured NPE by patch-clamp recording asdescribed in FIG. 1. Panel A. TREK-1 current is not detectable in NPE.Panel B. NPE were infected with a TREK-1 bearing adenovirus and currentwas recorded. Panel C. Summary of numerous trials.

FIG. 5. Expression of TREK-1 increases proliferation of normal prostateepithelial cells (NPE). Normal prostate epithelial cell cultures wereobtained from Clonetics and infected with a TREK-1-containingadenovirus. Some virally infected cells were also treated withsipatrigine (10 μM), a TREK-1 blocker. Cell proliferation was assessedusing the MTT assay as described in FIG. 3. These data are presented asmean±SEM from five paired experiments. * p<0.05, the NPE/TREK-1 groupdiffered significantly from each of the other treatments and no othergroups were different.

FIG. 6 Immunohistochemical staining of human prostate tissue revealsthat TREK-1 is over-expressed in cancer. Human tissue samples werestained with rabbit polyclonal anti-human TREK-1 antibody (Alomone).Panels A and B show a low power and high power view of the same field.Under the low power, a normal gland is visible (center right). Theepithelial cells lining the luminal surface are very lightly stained. Anadjacent cancerous gland (center left) shows a very small luminal spaceand the epithelial cells lining it are very densely stained indicatingan overexpression of TREK-1. The same features are visible under higherpower in Panel B.

FIG. 7. Meclofenamate activates TREK-1 current in CHO cells thatheterologously express the channel. CHO cells were transfected with aplasmid encoding human TREK-1 and the current was studied by patchclamp. The current-voltage relation was determined using a ramp protocolthat went from −130 mV to +40 mV in 6 s (after correction for thejunction potential). Current was greater in the presence ofmeclofenamate. This is typical of 7 cells.

FIG. 8. Trifluoperazine inhibits TREK-1 current in CHO cells thatheterologously express the channel. CHO cells were transfected with aplasmid encoding human TREK-1 and the current was studied by patchclamp. The current-voltage relation was determined using a ramp protocolthat went from −130 mV to +40 mV in 6 s (after correction for thejunction potential). Current was less in the presence oftrifluoperazine. This is typical of 3 cells.

FIG. 9. Structure of ONO-RS-082, BML263 and BLM 264.

FIG. 10. TREK-1 expression increases proliferation in CHO cells whichsignificantly correlates with current. CHO cells were transfected withTREK-1 using standard methods. Transfected cells were exposed tosipatrigine in doses from 0 to 100 uM and then tested for proliferationand for TREK-1 current by methods described elsewhere in thisapplication. The percent of control proliferation, as measured by theMTT assay, was plotted against the inhibition of TREK-1 current, asmeasured by patch clamp analysis. The data were then analyzed by linearregression which shows a significant correlation between the rate ofgrowth and the expression of current in these cells (p<0.0001).

FIG. 11. TREK-1 stable over-expressor cell lines have a significantlyhigher proliferation rate than control CHO cells. Several clones of CHOcells that over-express TREK-1 have been isolated as describedelsewhere. Each clone was tested for the expression of current (rightpanel) and for its proliferation rate (left panel).

FIG. 12. TREK-1 over-expression in CHO cells significantly increases thenumber of cells in S-phase. CHO cells were transfected with TREK-1 bystandard methods and then fixed for cell cycle analysis as describedelsewhere. Cells were analyzed by FACS analysis and compared to controlCHO cells, TREK-1 expressing cells had a significant shift from G0/G1 toS and G2/M.

FIG. 13. TREK-1 over-expression in CHO cells promotes anchorageindependent growth. Stable TREK-1 over-expressors were tested for growthin soft agar as described elsewhere. Top panel shows the absence ofcolonies formed by control cells (left) and the presence of manycolonies (red spots) formed by clones 6 (middle) and 10 (right). Amicrographic analysis of some of these colonies is shown in the bottompanel. Control cells can be seen (left) but these cells, while alive,are not dividing. Over-expressors, however, continue to grow even whensuspended in agar and a few examples of colonies formed of many cellsare shown (middle and right).

5. DETAILED DESCRIPTION OF THE INVENTION

Described herein is the discovery that the expression of two-pore K⁺channels is increased in tumor cells as compared to normal cells. Themethods and compositions of the invention may be used for diseasediagnosis, drug screening and treatment of cancer. The invention isdescribed in detail in the subsections below.

5.1. Diagnostic Methods

In various embodiments, the present invention provides a variety ofmethods for the diagnostic and prognostic evaluation of cancer. Suchmethods may, for example, utilize reagents such as the TREK-1 genenucleotide sequences and antibodies directed against TREK-1 geneproducts.

Specifically, such reagents may be used to detect the level of TREK-1expression, for example, for: (1) the detection of over-expression ofTREK-1 gene mRNA relative to normal cells; and/or (2) the detection ofan over-abundance of TREK-1 gene product relative to normal cells, eachof which correlates with cancer or a progression toward cancer ormetastasis.

Thus, the present invention provides a method for diagnosis and/orprognosis of cancer in a subject comprising: (a) detecting the level ofTREK-1 expression in a sample derived from a subject; and (b) comparingthe level of TREK-1 expression detected in the subject's sample to thelevel of TREK-1 expression detected in a control sample, wherein anincrease in the level of TREK-1 expression detected in the subject'ssample as compared to a control sample is an indicator of a subject withcancer or progression toward cancer.

The methods described herein may be applied to samples of cells orcellular materials taken directly from a patient. Any method known inthe art for collection or isolation of the desired cells or materialscan be used. In particular, for prostate, as well as breast, colon andbladder cancer, samples for testing may be obtained by techniques knownin the art.

The methods described herein may be performed, for example, by utilizingpre-packaged diagnostic test kits comprising at least one specificTREK-1 gene nucleic acid or anti-TREK-1 gene product antibody reagent,which may be conveniently used, e.g., in clinical settings or in homesettings, to diagnose patients exhibiting preneoplastic or neoplasticabnormalities, and to screen and identify those individuals exhibiting apredisposition to such neoplastic changes.

The present invention is useful for the diagnosis and prognosis ofmalignant diseases in which the TREK-1 gene or gene product isimplicated or is suspected to be implicated. Such malignancies includebut are not limited to cancer of the prostate gland, as well as cancerof the breast, colon and bladder. Nucleic acid-based detectiontechniques are described, below. Peptide detection techniques aredescribed, below.

Expression levels of the TREK-1 gene can be detected by utilizing anumber of techniques. For the detection of TREK-1 transcripts, any celltype or tissue in which the TREK-1 gene is expressed, such as, forexample, prostate cancer cells, including metastases, may be utilized.

In a preferred embodiment of the invention, quantitative aspects ofTREK-1 gene expression are assayed. For example, RNA from a cell type ortissue known, or suspected, to express the TREK-1 gene, such as prostatecancer cells, including metastases, may be isolated and tested utilizinghybridization or PCR techniques. Diagnostic methods for the detection ofaberrant TREK-1 gene expression can include hybridization techniqueswhich involve for example, contacting and incubating nucleic acids,including RNA molecules obtained from a sample, e.g., derived from apatient sample, with one or more labeled TREK-1 nucleic acid reagentsunder conditions favorable for the specific annealing of these reagentsto their complementary sequences within the TREK-1 RNA molecule.Preferably, the lengths of these TREK-1 nucleic acid reagents are atleast 15 to 30 nucleotides. After incubation, all non-annealed nucleicacids are removed from the nucleic acid:TREK-1 molecule hybrid. Thepresence of nucleic acids which have hybridized, if any such moleculesexist, is then detected. Using such a detection scheme, the nucleic acidfrom the cell type or tissue of interest can be immobilized, forexample, to a solid support such as a membrane, or a plastic surfacesuch as that on a microtitre plate or polystyrene beads. In this case,after incubation, non-annealed, labeled nucleic acid reagents are easilyremoved. Detection of the remaining, annealed, labeled TREK-1 nucleicacid reagents is accomplished using standard techniques well-known tothose in the art. The TREK-1 gene sequences to which the nucleic acidreagents have annealed can be compared to the annealing pattern expectedfrom a normal TREK-1 gene expressing cell in order to determine whetherthe TREK-1 gene is over-expressed.

In another embodiment of the invention, RT-PCR techniques can beutilized to detect differences in levels of TREK-1 transcripts which maybe due to normal or abnormal alternative splicing. TREK-1 nucleic acidsequences may be derived by performing PCR using two oligonucleotideprimers designed on the basis of the TREK-1 nucleotide sequencesdisclosed herein. The template for the reaction may be cDNA obtained byreverse transcription of mRNA prepared from cell lines or tissue knownto express TREK-1, i.e, prostate tumor cells.

Mammalian TREK-1 sequences that may be used in the design ofhybridization probes and/or PCR primers include, for example, thosedisclosed in Genebank accession number is NM001017424, Fink et al.(1996, EMBO Journal 15:6854-6862) or Meadows et al., (2000, PflugersArch. 439:714-22). The disclosures of these publications in theirentireties are hereby incorporated by reference into this application

Additionally, it is possible to perform such TREK-1 gene expressionassays “in situ”, i.e., directly upon tissue sections (fixed and/orfrozen) of patient tissue obtained from biopsies or resections, suchthat no nucleic acid purification is necessary. Nucleic acid reagentssuch as those described above may be used as probes and/or primers forsuch in situ procedures (see, for example, Nuovo, G. J., 1992, “PCR InSitu Hybridization: Protocols And Applications”, Raven Press, N.Y.).

Antibodies, and fragments thereof, directed against TREK-1 gene productmay also be used as diagnostics and prognostics, as described herein.Such diagnostic methods may be used to detect abnormalities in the levelof TREK-1 expression. Such antibodies and fragments thereof include, butare not limited to, naturally occurring antibodies, bivalent fragmentssuch as (Fab′)₂, monovalent fragments such as Fab, single chainantibodies, single chain Fv (scFv), single domain antibodies,multivalent single chain antibodies, diabodies, triabodies, and the likethat bind specifically with antigens.

Antibodies, and fragments thereof, to be used in the diagnostic andprognostic methods of the invention are those that bind specifically toan epitope of a mammalian TREK-1 protein. Such TREK-1 proteins include,for example, those having the amino acid sequences disclosed in Genebankaccession number is NM 001017424, Fink et al. (1996, EMBO Journal15:6854-6862) or Meadows et al., (2000, Pflugers Arch. 439:714-22). Forthe diagnostic and prognostic methods of the invention described below,a directly labeled anti-TREK-1 antibody may be utilized. Alternatively,an unlabeled anti-TREK-1 antibody may be utilized followed by indirectlabeling of the antibody with an anti-Ig antibody.

The tissue or cell type to be analyzed will generally include thosewhich are known, or suspected, to express the TREK-1 gene, such as, forexample, prostate, breast, colon or bladder cancer cells or metastaticcells. The protein isolation methods employed herein may, for example,be such as those described in Harlow and Lane (Harlow, E. and Lane, D.,1988, “Antibodies: A Laboratory Manual”, Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, N.Y.), which is incorporated herein byreference in its entirety.

Preferred diagnostic methods for the detection of TREK-1 gene productmay involve, for example, immunoassays wherein the TREK-1 gene productsare detected by their interaction with an anti-TREK-1 geneproduct-specific antibody. For example, antibodies, or fragments ofantibodies useful in the present invention may be used to quantitativelydetect the presence of TREK-1 gene product. The antibodies (or fragmentsthereof) useful in the present invention may, additionally, be employedhistologically, as in immunofluorescence or immunoelectron microscopy,for in situ detection of TREK-1 gene products. In situ detection may beaccomplished by removing a histological specimen from a patient, such asparaffin embedded sections of prostate tissue and applying thereto alabeled antibody of the present invention. The antibody (or fragment) ispreferably applied by overlaying the labeled antibody (or fragment) ontoa biological sample. It may also be desirable to introduce the antibodyinside the cell, for example, by making the cell membrane permeable.Through the use of such a procedure, it is possible to determine notonly the presence of the TREK-1 gene product but also its distributionin the examined tissue. Using the present invention, those of ordinaryskill will readily perceive that any of a wide variety of histologicalmethods (such as staining procedures) can be modified in order toachieve such in situ detection.

Immunoassays for TREK-1 gene product will typically comprise incubatinga sample, such as a biological fluid, a tissue extract, freshlyharvested cells, or lysates of cells, in the presence of an antibodycapable of identifying TREK-1 gene products and detecting the boundantibody by any of a number of techniques well-known in the art.

The biological sample may be brought in contact with and immobilizedonto a solid phase support or carrier such as nitrocellulose, or othersolid support which is capable of immobilizing cells, cell particles orsoluble proteins. The support may then be washed with suitable buffersfollowed by treatment with the detectably labeled TREK-1 gene specificantibody. The solid phase support may then be washed with the buffer asecond time to remove unbound antibody. The amount of bound label onsolid support may then be detected by conventional means.

By “solid phase support or carrier” is intended any support capable ofbinding an antigen or an antibody. Well-known supports or carriersinclude glass, polystyrene, polypropylene, polyethylene, dextran, nylon,amylases, natural and modified celluloses, polyacrylamides, gabbros, andmagnetite. The nature of the carrier can be either soluble to someextent or insoluble for the purposes of the present invention. Thesupport material may have virtually any possible structuralconfiguration so long as the coupled molecule is capable of binding toan antigen or antibody. Thus, the support configuration may bespherical, as in a bead, or cylindrical, as in the inside surface of atest tube, or the external surface of a rod. Alternatively, the surfacemay be flat such as a sheet, test strip, etc. Preferred supports includepolystyrene beads. Those skilled in the art will know many othersuitable carriers for binding antibody or antigen, or will be able toascertain the same by use of routine experimentation.

The binding activity of anti-TREK-1 gene product antibody may bedetermined according to well known methods. Those skilled in the artwill be able to determine operative and optimal assay conditions foreach determination by employing routine experimentation.

One of the ways in which the TREK-1 peptide-specific antibody can bedetectably labeled is by linking the same to an enzyme and use in anenzyme immunoassay (EIA) (Voller, A., “The Enzyme Linked ImmunosorbentAssay (ELISA)”, 1978, Diagnostic Horizons 2:1-7, MicrobiologicalAssociates Quarterly Publication, Walkersville, Md.); Voller et al.,1978, J. Clin. Pathol. 31:507-520; Butler 1981, Meth. Enzymol.73:482-523; Maggio, E. (ed.), 1980, Enzyme Immunoassay, CRC Press, BocaRaton, Fla.; Ishikawa, E. et al., (eds.), 1981, Enzyme Immunoassay,Kgaku Shoin, Tokyo). The enzyme which is bound to the antibody willreact with an appropriate substrate, preferably a chromogenic substrate,in such a manner as to produce a chemical moiety which can be detected,for example, by spectrophotometric, fluorimetric or by visual means.Enzymes which can be used to detectably label the antibody include, butare not limited to, malate dehydrogenase, staphylococcal nuclease,delta-5-steroid isomerase, yeast alcohol dehydrogenase,alpha-glycerophosphate dehydrogenase, triose phosphate isomerase,horseradish peroxidase, alkaline phosphatase, asparaginase, glucoseoxidase, beta-galactosidase, ribonuclease, urease, catalase,glucose-6-phosphate dehydrogenase, glucoamylase andacetylcholinesterase. The detection can be accomplished by colorimetricmethods which employ a chromogenic substrate for the enzyme. Detectionmay also be accomplished by visual comparison of the extent of enzymaticreaction of a substrate in comparison with similarly prepared standards.

Detection may also be accomplished using any of a variety of otherimmunoassays. For example, by radioactively labeling the antibodies orantibody fragments, it is possible to detect TREK-1 protein through theuse of a radioimmunoassay (RIA) (see, for example, Weintraub, B.,Principles of Radioimmunoassays, Seventh Training Course on RadioligandAssay Techniques, The Endocrine Society, March, 1986, which isincorporated by reference herein). The radioactive isotope can bedetected by such means as the use of a gamma counter or a scintillationcounter or by autoradiography.

It is also possible to label the antibody with a fluorescent compound.When the fluorescently labeled antibody is exposed to light of theproper wavelength, its presence can then be detected due tofluorescence. Among the most commonly used fluorescent labelingcompounds are fluorescein isothiocyanate, rhodamine, phycoerythrin,phycocyanin, allophycocyanin, o-phthaldehyde and fluorescamine.

The antibody can also be detectably labeled using fluorescence emittingmetals such as ¹⁵²Eu, or others of the lanthanide series. These metalscan be attached to the antibody using such metal chelating groups asdiethylenetriaminepentacetic acid (DTPA) or ethylenediaminetetraaceticacid (EDTA).

The antibody also can be detectably labeled by coupling it to achemiluminescent compound. The presence of the chemiluminescent-taggedantibody is then determined by detecting the presence of luminescencethat arises during the course of a chemical reaction. Examples ofparticularly useful chemiluminescent labeling compounds are luminol,isoluminol, theromatic acridinium ester, imidazole, acridinium salt andoxalate ester.

Likewise, a bioluminescent compound may be used to label the antibody ofthe present invention. Bioluminescence is a type of chemiluminescencefound in biological systems in, which a catalytic protein increases theefficiency of the chemiluminescent reaction. The presence of abioluminescent protein is determined by detecting the presence ofluminescence. Important bioluminescent compounds for purposes oflabeling are luciferin, luciferase and aequorin.

In various embodiments, the present invention provides the measurementof TREK-1 gene product, and the uses of such measurements in clinicalapplications. The measurement of TREK-1 gene product can be valuable indetecting and/or staging cancer in a subject, in screening of cancer ina population, in differential diagnosis of the physiological conditionof a subject, and in monitoring the effect of a therapeutic treatment ona subject

In an embodiment of the present invention, measurements of TREK-1 geneexpression can be used to stage the cancer in a subject. Staging refersto the grouping of patients according to the extent of their disease.Staging is useful in choosing treatment for individual patients,estimating prognosis, and comparing the results of different treatmentprograms. Staging of cancer is performed initially on a clinical basis,according to the physical examination and laboratory radiologicevaluation.

Any immunoassay, such as those described above, can be used to measurethe amount of TREK-1 gene expression which is compared to a baselinelevel. This baseline level can be the amount which is established to benormally present in the tissue or body fluid of subjects with variousdegrees of the disease or disorder. An amount present in the tissue orbody fluid of the subject which is similar for detection of theamplified product, the nucleic acid amplification may be performed usingradioactively or non-radioactively labeled nucleotides. Alternatively,enough amplified product may be made such that the product may bevisualized by standard ethidium bromide staining or by utilizing anyother suitable nucleic acid staining method. So a standard amount,established to be normally present in the tissue or body fluid of thesubject during a specific stage of cancer, is indicative of the stage ofthe disease in the subject. The baseline level could also be the levelpresent in the subject prior to the onset of disease or the amountpresent during remission of the disease.

In specific embodiments of this aspect of the invention, measurements oflevels of the TREK-1 gene product can be used in the detection ofprostate cancer or the presence of metastases or both. In yet anotherembodiment of the invention, measurements of levels of the TREK-1 geneproduct can be used in the detection breast, colon and bladder cancer.

The present invention also provides a method for monitoring the effectof a therapeutic treatment on a subject who has undergone thetherapeutic treatment. TREK-1 gene product can be identified anddetected in cancer patients with different manifestations of disease,providing a sensitive assay to monitor therapy. The therapeutictreatments which may be evaluated according to the present inventioninclude but are not limited to radiotherapy, surgery, chemotherapy,vaccine administration, endocrine therapy, immunotherapy, and genetherapy, etc.

The method of the invention comprises measuring at suitable timeintervals before, during, or after therapy, the amount of a TREK-1 geneexpression. Any change or absence of change in the amount of the TREK-1gene expression can be identified and correlated with the effect of thetreatment on the subject, such as, for example, a reduction of thetransformed phenotype in cancer cells.

In a preferred aspect, the approach that can be taken is to determinethe levels of TREK-1 gene expression levels at different time points andto compare these values with a baseline level. The baseline level can beeither the level of the marker present in normal, disease freeindividuals; and/or the levels present prior to treatment, or duringremission of disease, or during periods of stability. These levels canthen be correlated with the disease course or treatment outcome.Elevated levels of TREK-1 gene expression relative to the baseline levelindicates a poor response to treatment.

5.2. Screening Assays for Compounds that Modulate TREK-1 Activity

The present invention further provides methods for the identification ofcompounds that may, through their interaction with the TREK-1 gene orTREK-1 gene product, affect the onset, progression and metastatic spreadof cancer; especially prostate cancer.

The following assays are designed to identify: (i) compounds that bindto TREK-1 gene products; (ii) compounds that bind to other intracellularproteins that interact with a TREK-1 gene product; and (iii) compoundsthat modulate the activity of TREK-1 gene (i.e., modulate the level ofTREK-1 gene expression and/or modulate the level of TREK-1 gene productactivity). Compounds identified via assays such as those describedherein may be useful, for example, in elaborating the biologicalfunctions of the TREK-1 gene product, and for ameliorating symptoms ofcancer. It is to be noted that the compositions of the invention includepharmaceutical compositions comprising one or more of the compoundsidentified via such methods. Such pharmaceutical compositions can beformulated, for example, as discussed, below.

Assays may be utilized which identify compounds which bind to TREK-1gene regulatory sequences (e.g., promoter sequences) and which maymodulate the level of TREK-1 gene expression. Such methods foridentifying compounds that modulate TREK-1 gene expression, comprise,for example: (a) contacting a test compound with a cell or cell lysatecontaining a reporter gene operatively associated with a TREK-1 generegulatory element; and (b) detecting expression of the reporter geneproduct. Also provided is another method for identifying compounds thatmodulate TREK-1 gene expression comprising: (a) contacting a testcompound with a cell containing TREK-1 transcripts; and (b) detectingthe translation of the TREK-1 transcript. Any reporter gene known in theart can be used, such as but not limited to, green fluorescent protein,β-galactosidase, alkaline phosphatase, chloramphenicolacetyltransferase, etc.

In yet another embodiment of the invention, in vitro systems may bedesigned to identify compounds capable of interacting with, e.g.,binding to, the TREK-1 gene product. Such compounds may be useful, forexample, in modulating the activity of TREK-1 gene product, inelaborating the biological function of the TREK-1 gene product, or maybe utilized in screens for identifying compounds that disrupt normalTREK-1 gene product interactions, or may in themselves disrupt suchinteractions.

The principle of the assays used to identify compounds that interactwith the TREK-1 gene product involves preparing a reaction mixture ofthe TREK-1 gene product, or fragments thereof and the test compoundunder conditions and for a time sufficient to allow the two componentsto interact with, e.g., bind to, thus forming a complex, which canrepresent a transient complex, which—can be removed and/or detected inthe reaction mixture. These assays can be conducted in a variety ofways. For example, one method to conduct such an assay would involveanchoring TREK-1 gene product or the test substance onto a solid phaseand detecting TREK-1 gene product/test compound complexes anchored onthe solid phase at the end of the reaction. In one embodiment of such amethod, the TREK-1 gene product or fragment thereof may be anchored ontoa solid surface, and the test compound, which is not anchored, may belabeled, either directly or indirectly.

In yet another embodiment of the invention, displacement assays may beused to identify compounds that interact with the TREK-1 gene product,or fragments thereof. The assay is based on the ability of suchcompounds to displace or preventing binding of compounds known tointeract with the TREK-1 gene product or fragments thereof.

The basic principle of the displacement assay system used to identifycompounds that interact with the TREK-1 gene product or fragmentsthereof involves preparing a reaction mixture containing the TREK-1 geneproduct, or fragments thereof, and the compound know to bind to TREK-1under conditions and for a time sufficient to allow the two to interactand bind, thus forming a complex. In order to test a compound forinhibitory activity, the reaction mixture is prepared in the presenceand absence of the test compound. The test compound may be initiallyincluded in the reaction mixture, or may be added at a time subsequentto the addition of TREK-1 gene product and its intracellular interactingpartner. Control reaction mixtures are incubated without the testcompound or with a placebo. The formation of any complexes between theTREK-1 gene product or fragments thereof and the compound known to bindto TREK-1 is then detected. The formation of a complex in the controlreaction, but not in the reaction mixture containing the test compound,indicates that the compound interferes with the interaction of theTREK-1 gene product and the compound known to bind to TREK-1.

The assay for compounds that interfere with the interaction of theTREK-1 gene product and compounds known to bind to TREK-1 can beconducted in a heterogeneous or homogeneous format. Heterogeneous assaysinvolve anchoring either the TREK-1 gene product or the compound knownto bind to TREK-1 onto a solid phase and detecting complexes anchored onthe solid phase at the end of the reaction. In homogeneous assays, theentire reaction is carried out in a liquid phase. In either approach,the order of addition of reactants can be varied to obtain differentinformation about the compounds being tested. For example, testcompounds that interfere with the interaction between the TREK-1 geneproducts and the compounds known to bind to TREK-1, e.g., bycompetition, can be identified by conducting the reaction in thepresence of the test substance; i.e., by adding the test substance tothe reaction mixture prior to or simultaneously with the TREK-1 geneprotein and compound known t bind to TREK-1. Alternatively, testcompounds that disrupt preformed complexes, e.g. compounds with higherbinding constants that displace one of the components from the complex,can be tested by adding the test compound to the reaction mixture aftercomplexes have been formed.

In a specific embodiment of the invention, compounds know to bind toTREK-1, that may be used in the practice of the invention include, forexample, ONO-RS-082, BML263 and BLM 264 (FIG. 9). To facilitate thedetection of such compounds, the compounds may be radioactively orfluorescently labeled.

In a specific embodiment of the invention, membrane preparations derivedfrom cells known to express TREK-1, or genetically engineered to expressTREK-1, may be used in the displacement assays of the invention. In yetanother embodiment of the invention, membrane preparations may bederived from tissues derived from transgenic animals engineered toexpress TREK-1.

In practice, microtitre plates may conveniently be utilized as the solidphase. The anchored component may be immobilized by non-covalent orcovalent attachments. Non-covalent attachment may be accomplished bysimply coating the solid surface with a solution of the protein anddrying. Alternatively, an immobilized antibody, preferably a monoclonalantibody, specific for the protein to be immobilized may be used toanchor the protein to the solid surface. The surfaces may be prepared inadvance and stored.

In order to conduct the assay, the nonimmobilized component is added tothe coated surface containing the anchored component. After the reactionis complete, unreacted components are removed (e.g., by washing) underconditions such that any complexes formed will remain immobilized on thesolid surface. The detection of complexes anchored on the solid surfacecan be accomplished in a number of ways. Where the previouslynonimmobilized component is pre-labeled, the detection of labelimmobilized on the surface indicates that complexes were formed. Wherethe previously nonimmobilized component is not pre-labeled, an indirectlabel can be used to detect complexes anchored on the surface; e.g.,using a labeled antibody specific for the previously nonimmobilizedcomponent (the antibody, in turn, may be directly labeled or indirectlylabeled with a labeled anti-Ig antibody).

Alternatively, a reaction can be conducted in a liquid phase, thereaction products separated from unreacted components, and complexesdetected; e.g., using an immobilized antibody specific for TREK-1 geneproduct or the test compound to anchor any complexes formed in solution,and a labeled antibody specific for the other component of the possiblecomplex to detect anchored complexes.

In another embodiment of the invention, assays may be utilized toidentify intracellular proteins that interact with the TREK-1 geneproduct. Any method suitable for detecting protein-protein interactionsmay be employed for identifying TREK-1 protein-intracellular proteininteractions. Among the traditional methods which may be employed areco-immunoprecipitation, crosslinking and co-purification throughgradients or chromatographic columns. Utilizing procedures such as theseallows for the isolation of intracellular proteins which interact withTREK-1 gene product. Once isolated, such an intracellular protein can beidentified and can, in turn, be used, in conjunction with standardtechniques, to identify additional proteins with which it interacts.

Assays may also be utilized to identify compounds that interfere withTREK-1 gene product/intracellular macromolecular interactions. TREK-1gene product may, in vivo, interact with one or more intracellularmacromolecules, such as proteins and nucleic acid molecules. Forpurposes of this discussion, such intracellular macromolecules arereferred to herein as “interacting partners.” Compounds that disruptTREK-1 interactions in this way may be useful in regulating the activityof the TREK-1 gene product.

The basic principle of the assay systems used to identify compounds thatinterfere with the interaction between the TREK-1 gene product and itsintracellular interacting partner or partners involves preparing areaction mixture containing the TREK-1 gene product, or fragmentsthereof, and the interacting partner under conditions and for a timesufficient to allow the two to interact and bind, thus forming acomplex. In order to test a compound for inhibitory activity, thereaction mixture is prepared in the presence and absence of the testcompound. The test compound may be initially included in the reactionmixture, or may be added at a time subsequent to the addition of TREK-1gene product and its intracellular interacting partner. Control reactionmixtures are incubated without the test compound or with a placebo. Theformation of any complexes between the TREK-1 gene product or fragmentsthereof and the intracellular interacting partner is then detected. Theformation of a complex in the control reaction, but not in the reactionmixture containing the test compound, indicates that the compoundinterferes with the interaction of the TREK-1 gene product and theinteracting partner.

The assay for compounds that interfere with the interaction of theTREK-1 gene product and interacting partners can be conducted in aheterogeneous or homogeneous format. Heterogeneous assays involveanchoring either the TREK-1 gene product or the binding partner onto asolid phase and detecting complexes anchored on the solid phase at theend of the reaction. In homogeneous assays, the entire reaction iscarried out in a liquid phase. In either approach, the order of additionof reactants can be varied to obtain different information about thecompounds being tested. For example, test compounds that interfere withthe interaction between the TREK-1 gene products and the interactingpartners, e.g., by competition, can be identified by conducting thereaction in the presence of the test substance; i.e., by adding the testsubstance to the reaction mixture prior to or simultaneously with theTREK-1 gene protein and intracellular interacting partner.Alternatively, test compounds that disrupt preformed complexes, e.g.compounds with higher binding constants that displace one of thecomponents from the complex, can be tested by adding the test compoundto the reaction mixture after complexes have been formed.

In yet another embodiment of the invention, cell-based assays may beused for identification of compounds which modulate TREK-1 activity andwhich may be used in treating cancer by modulating TREK-1 activity.Specifically, such assays identify compounds which affectTREK-1-dependent processes, such as but not limited to the manifestationof a transformed phenotype, i.e, changes in cell morphology, celldivision, differentiation, adhesion, motility, or phosphorylation,dephosphorylation of cellular proteins. Other TREK-1-dependent processeswhich may be affected include but are not limited to stimulation of K+channel activity. For example, changes in channel activity may bemeasured by changes in net current by patch clamp recording or changesin resting membrane potential. Compounds identified via such methodscan, for example, be utilized in methods for treating cancer andmetastasis.

In an embodiment, cell-based assays are based on expression of theTREK-1 gene product in a mammalian cell and measuring theTREK-1-dependent process. Any mammalian cell that can express the TREK-1gene and allow the functioning of the TREK-1 gene product can be used,in particular, cancer cells derived from the prostate, such as PC-3 andLNCaP may be used. Other cancer cell lines such as those derived frombreast, lung, colon, or other epithelial-derived cancers, may also beused provided that a detectable TREK-1 gene product is produced.Additionally, cells may be recombinantly engineered to express theTREK-1 gene using methods well known to those of skill in the art. Inthese assays, cells producing functional TREK-1 gene products areexposed to a test compound for an interval sufficient for the compoundto modulate the activity of the TREK-1 gene product. The activity ofTREK-1 gene product can be measured directly or indirectly through thedetection or measurement of TREK-1-dependent cellular processes such as,for example, the manifestation of a transformed phenotype. As a control,a cell not producing the TREK-1 gene product may be used forcomparisons. Depending on the cellular process, any techniques known inthe art may be applied to detect or measure it.

As disclosed above, over-expression of TREK-1 can result in an increasein cell proliferation. In contrast, decreasing the TREK-1 mediatedcurrent may slow proliferation. Accordingly, the present inventionprovides methods for identifying modulators of TREK-1 activity based oncell proliferation assays. For example, TREK-1 expressing cells may begrown in a 96-well plate and exposed to varying concentrations of a testsubstance for 4-24 h followed by measurement of cell proliferation.

Cells that may be utilized in the proliferation assays of the inventioninclude cells over-expressing TREK-1 wherein said over-expressionresults in an increase in cell proliferation. Such cells include cellsthat naturally over-express TREK-1 as well as cells geneticallyengineered to overexpress TREK-1. Cells include, for example, PC-3 cellsas well as CHO cells transfected with the TREK-1 gene. As demonstratedherein, CHO cells over-expressing TREK-1 have increased proliferationrates and acquire a tumorigenic phenotype, i.e., they exhibit anchorageindependent growth. Thus, in a preferred embodiment of the inventiongenetically engineered CHO cells may be used in the proliferation assaysof the invention.

Methods of measuring cell proliferation are well known in the art andmost commonly include determining DNA synthesis characteristic of cellreplication. There are numerous methods in the art for measuring DNAsynthesis, any of which may be used according to the invention. Forexample, DNA synthesis may be determined using a radioactive label([³H]thymidine) or labeled nucleotide analogues (BrdU) for detection byimmunofluorescence. Alternatively, the rate of proliferation can bemeasured using any of a number of commercial colorimetric kits, such asthe MTT assay. Additionally, the cells may be assayed to determinewhether there are changes in levels, or modification, of proteins knownto be associated with cell proliferation. Such proteins include, forexample, cyclin D1, CDK4 or p107. The efficacy of the test compound canbe assessed by generating dose response curves from data obtained usingvarious concentrations of the test compound. A control assay can also beperformed to provide a baseline for comparison. Compounds which arefound to alter cell proliferation may then be screened in anelectrophysiological assay to confirm that the effect is due tomodulation of TREK-1.

Using such proliferation assays, non-narcotic analgesics/non-steroidalanti-inflammatory drugs (NSAIDs) were identified as a class of compoundscapable of positive modulation of TREK-1 activity. Accordingly, NSAIDshaving the following general structure:

where R₁-R₉ may be the same or different and are selected from the groupconsisting of hydrogen, halogen, alkyl, or haloalkyl, may be used tomodulate the proliferation of cells. The free —COOH group may also be inthe form of a pharmaceutically acceptable salt or ester.

In a specific embodiment of the invention, Meclofenamic acid having themolecular formula C₁₄H₁₁Cl₂O₂N and the following chemical structure:

may be used to modulate the activity of TREK-1.

Using proliferation assays, tricyclic antipsychotics were identified asa class of compounds capable of negative modulation of TREK-activity.Accordingly, in an embodiment of the present invention, a TREK-1inhibitor may be a compound selected from the group consisting of one ormore tricyclic antipsychotics, tricyclic antidepressants, thiazines,dibenzoxazepines. In preferred embodiments, the compound is selectedfrom the group consisting of tricyclic thiazines, phenothiazines,thioxanthenes, more preferable from the group consisting ofphenothiazines. In one of the more preferred embodiments the TREK-1inhibitor is the tricyclic antipsychotic phenothiazine Trifluoperazine.

In instances where specific drug use is associated with behavioraleffects, the drug may be modified so that it maintains the ability tomodulate TREK-1 activity while minimized the CNS effect.

Compounds which may be screened in accordance with the inventioninclude, but are not limited to, small organic or inorganic compounds,peptides, antibodies and fragments thereof, and other organic compoundse.g., peptidomimetics) that modulate TREK-1 activity. Compounds mayinclude, but are not limited to, peptides such as, for example, solublepeptides, including but not limited to members of random peptidelibraries (see, e.g., Lam, K. S. et al., 1991, Nature 354:82-84;Houghten, R. et al., 1991, Nature 354:84-86); and combinatorialchemistry-derived molecular library made of D- and/or L-configurationamino acids, phosphopeptides (including, but not limited to, members ofrandom or partially degenerate, directed phosphopeptide libraries; (see,e.g., Songyang, Z. et al., 1993, Cell 72:767-778), antibodies(including, but not limited to, polyclonal, monoclonal, humanized,anti-idiotypic, chimeric or single chain antibodies, and FAb, F(ab′)₂and FAb expression library fragments, and epitope binding fragmentsthereof), and small organic or inorganic molecules.

5.3. Methods of Treating Proliferative Disorders

Described below are methods and compositions for treating cancer whereinthe TREK-1 gene or gene product is used as a therapeutic target. Suchcompositions include, but are not limited to, peptides, includingsoluble peptides, small organic or inorganic molecules, therapeuticnucleic acid molecules, including antisense, ribozymes and siNA, all ofwhich function as TREK-1 inhibitors. Additionally, anti-TREK-1antibodies, or fragments thereof, may be used to treat cancer. Suchantibodies and fragments thereof include, but are not limited to,naturally occurring antibodies, bivalent fragments such as (Fab′)₂,monovalent fragments such as Fab, single chain antibodies, single chainFv (scFv), single domain antibodies, multivalent single chainantibodies, diabodies, triabodies, and the like that bind specificallywith antigens.

The outcome of a treatment is designed to produce in a treated subject ahealthful benefit, which in the case of cancer, includes but is notlimited to remission of the cancer, palliation of the symptoms of thecancer, control of metastatic spread of the cancer. All such methodsinvolve modulating TREK-1 gene activity and/or expression which in turnmodulate the phenotype of the treated cell.

As discussed, above, successful treatment of cancer can be brought aboutby techniques which serve to decrease TREK-1 activity. Activity can bedecreased by, for example, directly decreasing TREK-1 gene productactivity and/or by decreasing the level of TREK-1 gene expression.Compounds that may be used to decrease TREK-1 activity include, but arenot limited to, oleylamine, sipatrigine or trifluoperazine.Additionally, compounds that inhibit the activity of phospholipase A2 or15-lipoxygenase (15-LOX) isozymes may be utilized to inhibit theproliferation of cancer cells.

For example, compounds such as those identified through assays describedabove, which decrease TREK-1 activity, can be used in accordance withthe invention to treat cancer. Such compounds can include, but are notlimited to peptides, including soluble peptides, and small organic orinorganic compounds, and can be referred to as TREK-1 inhibitors.

It should be understood that compounds capable of modulating TREK-1activity, as disclosed herein, include functional derivatives andanalogs, including pharmaceutically acceptable salts, esters, orhydrates thereof.

In the context of the invention, preference is given to pharmaceuticallyacceptable salts. “Pharmaceutically acceptable salts” refers to an acidaddition salt or a basic addition salt of a compound of the invention inwhich the resulting counter ion is understood in the art to be generallyacceptable for pharmaceutical uses. Pharmaceutically acceptable saltscan be salts of the compounds according to the invention with inorganicor organic acids. Preference is given to salts with inorganic acids,such as, for example, hydrochloric acid, hydrobromic acid, phosphoricacid or sulfuric acid, or to salts with organic carboxylic or sulfonicacids, such as, for example, acetic acid, maleic acid, fumaric acid,malic acid, citric acid, tartaric acid, lactic acid, benzoic acid, ormethanesulfonic acid, ethanesulfonic acid, phenylsulfonic acid,toluenesulfonic acid or naphthalenedisulfonic acid. Pharmaceuticallyacceptable salts can also be metal or ammonium salts of the compoundsaccording to the invention. Particular preference is given to, forexample, sodium, potassium, magnesium or calcium salts, and also toammonium salts which are derived from ammonia or organic amines, suchas, for example, ethylamine, di- or triethylamine, di- ortriethanolamine, dicyclohexylamine, dimethylaminoethanol, arginine,lysine, ethylenediamine or 2-phenylethylamine. (see, Berge et al. J.Pharm. Sci. 1977, 66, 1-19.)

The substances according to the invention may also be present aspharmaceutically acceptable ester, such as the methyl ester, ethyl esterand the like.

When one or more chiral centers are present in the compounds of thepresent invention, the individual isomers and mixtures thereof (e.g.,racemates, etc.) are intended to be encompassed by the formulae depictedherein. In certain embodiments, compounds of the invention may exist inseveral tautomeric forms. Accordingly, the chemical structures depictedherein encompass all possible tautomeric forms of the illustratedcompounds. Compounds of the invention may exist in various hydratedforms.

In an embodiment of the invention, the level of TREK-1 expression can bemodulated using TREK-1 based oligonucleotide molecules including but notlimited to antisense, ribozyme, or RNAi approaches to inhibit or preventtranslation of TREK-1 mRNA transcripts or triple helix approaches toinhibit transcription of the TREK-1 gene (herein after referred to as“therapeutic nucleic acid molecules”). Antisense, RNAi and ribozymeapproaches involve the design of oligonucleotides (either DNA or RNA)that are complementary to TREK-1 mRNA. The antisense, siNA or ribozymeoligonucleotides will be targeted to complementary TREK-1 mRNAtranscripts and prevent translation. Absolute complementarity, althoughpreferred, is not required. One skilled in the art can ascertain atolerable degree of mismatch by use of standard procedures to determinethe melting point of the hybridized complex. Mammalian TREK-1 sequencesthat may be used in the design of antisense, RNAi and ribozymes includethose disclosed in Genebank accession number is NM001017424, Fink et al.(1996, EMBO Journal 15:6854-6862) or Meadows et al., (2000, PflugersArch. 439:714-22).

In a preferred embodiment of the invention, double-stranded shortinterfering nucleic acid (siNA) molecules may be designed to inhibitTREK-1 expression. In one embodiment, the invention features adouble-stranded siNA molecule that down-regulates expression of theTREK-1 gene product, wherein said siNA molecule comprises about 15 toabout 28 base pairs.

In one embodiment, the invention features a double stranded shortinterfering nucleic acid (siNA) molecule that directs cleavage of aTREK-1 RNA via RNA interference (RNAi), wherein the double stranded siNAmolecule comprises a first and a second strand, each strand of the siNAmolecule is about 18 to about 28 nucleotides in length, the first strandof the siNA molecule comprises nucleotide sequence having sufficientcomplementarity to the TREK-1 RNA for the siNA molecule to directcleavage of the TREK-1 RNA via RNA interference, and the second strandof said siNA molecule comprises nucleotide sequence that iscomplementary to the first strand.

The use of antisense molecules as inhibitors of gene expression is aspecific, genetically based therapeutic approach (for a review, seeStein, in Ch. 69, Section 5 “Cancer: Principle and Practice ofOncology”, 4th ed., ed. by DeVita et al., J. B. Lippincott, Philadelphia1993). The present invention provides the therapeutic use of nucleicacids of at least six nucleotides that are antisense to the TREK-1 geneor a portion thereof. An “antisense” TREK-1 nucleic acid as used hereinrefers to a nucleic acid capable of hybridizing to a portion of a TREK-1RNA (preferably mRNA) by virtue of some sequence complementarity.

The antisense nucleic acid of the invention may be complementary to acoding and/or noncoding region of a TREK-1 mRNA. The antisense moleculeswill bind to the complementary TREK-1 gene mRNA transcripts and reduceor prevent translation. Absolute complementarity, although preferred, isnot required. A sequence “complementary” to a portion of an RNA, asreferred to herein, means a sequence having sufficient complementarityto be able to hybridize with the RNA, forming a stable duplex; in thecase of double-stranded antisense nucleic acids, a single strand of theduplex DNA may thus be tested, or triplex formation may be assayed. Theability to hybridize will depend on both the degree of complementarityand the length of the antisense nucleic acid. Generally, the longer thehybridizing nucleic acid, the more base mismatches with an RNA it maycontain and still form a stable duplex (or triplex, as the case may be).One skilled in the art can ascertain a tolerable degree of mismatch byuse of standard procedures to determine the melting point of thehybridized complex.

In yet another embodiment of the invention, ribozyme molecules designedto catalytically cleave TREK-1 mRNA transcripts can also be used toprevent translation of TREK-1 mRNA and expression of TREK-1. (See, e.g.,PCT International Publication WO90/11364, published Oct. 4, 1990; Sarveret al., 1990, Science 247:1222-1225).

Ribozymes are enzymatic RNA molecules capable of catalyzing the specificcleavage of RNA (For a review see, for example Rossi, J., 1994, CurrentBiology 4:469-471). The mechanism of ribozyme action involves sequencespecific hybridization of the ribozyme molecule to complementary targetRNA, followed by an endonucleolytic cleavage. The composition ofribozyme molecules must include one or more sequences complementary tothe target gene mRNA, and must include the well known catalytic sequenceresponsible for mRNA cleavage. For this sequence, see U.S. Pat. No.5,093,246, which is incorporated by reference herein in its entirety. Assuch, within the scope of the invention are engineered hammerhead motifribozyme molecules that specifically and efficiently catalyzeendonucleolytic cleavage of RNA sequences encoding target gene proteins.

Ribozyme molecules designed to catalytically cleave TREK-1 gene mRNAtranscripts can also be used to prevent translation of TREK-1 gene mRNAand expression of target or pathway gene. (See, e.g., PCT InternationalPublication WO90/11364, published Oct. 4, 1990; Sarver et al., 1990,Science 247:1222-1225). While ribozymes that cleave mRNA at sitespecific recognition sequences can be used to destroy TREK-1 gene mRNAs,the use of hammerhead ribozymes is preferred Hammerhead ribozymes cleavemRNAs at locations dictated by flanking regions that form complementarybase pairs with the target mRNA. The sole requirement is that the targetmRNA have the following sequence of two bases: 5′-UG-3′. Theconstruction and production of hammerhead ribozymes is well known in theart and is described more fully in Haseloff and Gerlach, 1988, Nature,334:585-591. Preferably the ribozyme is engineered so that the cleavagerecognition site is located near the 5′ end of the TREK-1 gene mRNA;i.e., to increase efficiency and minimize the intracellular accumulationof non-functional mRNA transcripts.

The ribozymes of the present invention also include RNAendoribonucleases (hereinafter “Cech-type ribozymes”) such as the onewhich occurs naturally in Tetrahymena thermophila (known as the IVS, orL-19 IVS RNA) and which has been extensively described by Thomas Cechand collaborators (Zaug, et al., 1984, Science, 224:574-578; Zaug andCech, 1986, Science, 231:470-475; Zaug, et al., 1986, Nature,324:429-433; published International patent application No. WO 88/04300by University Patents Inc.; Been and Cech, 1986, Cell, 47:207-216). TheCech-type ribozymes have an eight base pair active site which hybridizesto a target RNA sequence whereafter cleavage of the target RNA takesplace. The invention encompasses those Cech-type ribozymes which targeteight base-pair active site sequences that are present in a TREK-1 gene.

Alternatively, endogenous TREK-1 gene expression can be reduced bytargeting deoxyribonucleotide sequences complementary to the regulatoryregion of the TREK-1 gene (i.e., the TREK-1 promoter and or enhancer) toform triple helical structures that prevent transcription of the TREK-1gene in targeted tumor cells in the body. (See generally, Helene, C. etal., 1991, Anticancer Drug Des. 6:569-584 and Maher, I J, 1992,Bioassays 14:807-815).

Therapeutic nucleic acid molecules such as RNAi, antisense and ribozymemolecules which inhibit TREK-1 gene expression can be used in accordancewith the invention to reduce the level of TREK-1 gene expression,thereby effectively reducing the level of TREK-1 activity. Stillfurther, triple helix molecules can be utilized in reducing the level ofTREK-1 gene activity.

Such therapeutic nucleic acid molecules, i.e., RNAi, antisense, ribozymeand triple helix forming oligonucleotides, may be synthesized usingstandard methods known in the art for the synthesis of DNA and RNAmolecules. These include techniques for chemically synthesizingoligodeoxyribonucleotides and oligoribonucleotides, such as for example,solid phase phosphoramidite chemical synthesis. The nucleic acidmolecule can be DNA or RNA or chimeric mixtures or derivatives ormodified versions thereof, single-stranded or double-stranded. Thenucleic acid molecule can be modified at the base moiety, sugar moiety,or phosphate backbone, for example, to improve stability of themolecule, hybridization, etc. The nucleic acid molecule may includeother appended groups such as peptides (e.g., for targeting host cellreceptors in vivo), or agents facilitating transport across the cellmembrane (see, e.g., Letsinger et al., 1989, Proc. Natl. Acad. Sci.U.S.A. 86:6553-6556; Lemaitre et al., 1987, Proc. Natl. Acad. Sci.84:648-652; PCT Publication No. WO88/09810, published Dec. 15, 1988),hybridization-triggered cleavage agents. (See, e.g., Krol et al., 1988,BioTechniques 6:958-976) or intercalating agents. (See, e.g., Zon, 1988,Pharm. Res. 5:539-549). To this end, the nucleic acid molecules may beconjugated to another molecule, e.g., a peptide, hybridization triggeredcross-linking agent, transport agent, hybridization-triggered cleavageagent, etc.

Alternatively, the therapeutic nucleic acid molecules can be generatedby in vitro and in vivo transcription of DNA sequences encoding thetherapeutic nucleic acid molecules. Such DNA sequences can beincorporated into a wide variety of vectors which incorporate suitableRNA polymerase promoters such as the T7 or SP6 polymerase promoters.

Any technique which serves to selectively administer nucleic acidmolecules to a cell population of interest can be used, for example, byusing a delivery complex. Such a delivery complex can comprise anappropriate nucleic acid molecule and a targeting means. Such targetingmeans can comprise, for example, sterols, lipids, viruses or target cellspecific binding agents. In a specific embodiment, pharmaceuticalcompositions comprising a therapeutic nucleic acid molecule areadministered via biopolymers, liposomes, microparticles, ormicrocapsules. In various embodiments of the invention, it may be usefulto use such compositions to achieve sustained release of the therapeuticnucleic acids. In a specific embodiment, it may be desirable to utilizeliposomes targeted via antibodies to specific identifiable tumorantigens (Leonetti et al., 1990, Proc. Natl. Acad. Sci. U.S.A.87:2448-2451; Renneisen et al., 1990, J. Biol. Chem. 265:16337-16342).

It is often difficult to achieve intracellular concentrations of thetherapeutic nucleic acid molecule sufficient to suppress translation ofendogenous mRNAs. Therefore, a preferred approach utilizes a recombinantDNA construct in which expression of the therapeutic nucleic acidmolecule is placed under the control of a strong pol III or pol IIpromoter. For general reviews of the methods of gene therapy, seeGoldspiel et al., 1993, Clinical Pharmacy 12:488-505; Wu and Wu, 1991,Biotherapy 3:87-95; Tolstoshev, 1993, Ann. Rev. Pharmacol. Toxicol.32:573-596; Mulligan, 1993, Science 260:926-932; and Morgan andAnderson, 1993, Ann Rev. Biochem. 62:191-217; May, 1993, TIBTECH11(5):155-215). Methods commonly known in the art of recombinant DNAtechnology which can be used are described in Ausubel et al. (eds.),1993, Current Protocols in Molecular Biology, John Wiley & Sons, NY;Kriegler, 1990, Gene Transfer and Expression, A Laboratory Manual,Stockton Press, NY; and in Chapters 12 and 13, Dracopoli et al. (eds.),1994, Current Protocols in Human Genetics, John Wiley & Sons, NY.

The use of recombinant DNA constructs to transfect target cells in thepatient will result in the transcription of sufficient amounts of thetherapeutic nucleic acid molecule that will form complementary basepairs with the endogenous TREK-1 gene transcripts and thereby preventtranslation of the TREK-1 gene mRNA. For example, a vector can beintroduced in vivo such that it is taken up by a cell and directs thetranscription of an antisense RNA. Such a vector can remain episomal orbecome chromosomally integrated, as long as it can be transcribed toproduce the desired antisense RNA.

Such vectors can be constructed by recombinant DNA technology methodsstandard in the art. Vectors can be plasmid, viral, or others known inthe art, used for replication and expression in mammalian cells.Expression of the sequence encoding a therapeutic nucleic acid can be byany promoter known in the art to act in mammalian, preferably humancells. Such promoters can be inducible or constitutive. Such promotersinclude but are not limited to: the SV40 early promoter region (Bernoistand Chambon, 1981, Nature 290:304-310), the promoter contained in the 3′long terminal repeat of Rous sarcoma virus (Yamamoto et al., 1980, Cell22:787-797), the herpes thymidine kinase promoter (Wagner et al., 1981,Proc. Natl. Acad. Sci. U.S.A. 78:1441-1445), the regulatory sequences ofthe metallothionein gene (Brinster et al., 1982, Nature 296:39-42), etc.Any type of plasmid, cosmid, YAC or viral vector can be used to preparethe recombinant DNA construct which can be introduced either directlyinto the tissue site, or via a delivery complex. Alternatively, viralvectors can be used which selectively infect the desired tissue.

In a specific embodiment, a viral vector that contains the nucleic acidof interest, i.e., a therapeutic nucleic acid molecule is used. Forexample, a retroviral vector can be used (see Miller et al., 1993, Meth.Enzymol. 217:581-599). These retroviral vectors have been modified todelete retroviral sequences that are not necessary for packaging of theviral genome and integration into host cell DNA. The TREK-1 nucleic acidto be used in gene therapy is cloned into the vector, which facilitatesdelivery of the gene into a patient. More detail about retroviralvectors can be found in Boesen et al., 1994, Biotherapy 6:291-302, whichdescribes the use of a retroviral vector to deliver the mdr1 gene tohematopoietic stem cells in order to make the stem cells more resistantto chemotherapy. Other references illustrating the use of retroviralvectors in gene therapy are: Clowes et al., 1994, J. Clin. Invest.93:644-651; Kiem et al., 1994, Blood 83:1467-1473; Salmons and Gunzberg,1993, Human Gene Therapy 4:129-141; and Grossman and Wilson, 1993, Curr.Opin. in Genetics and Devel. 3:110-114.

Adenoviruses are other viral vectors that can be used in gene therapy.Adenoviruses are especially attractive vehicles for delivering genes torespiratory epithelia. Adenoviruses naturally infect respiratoryepithelia where they cause a mild disease. Other targets foradenovirus-based delivery systems are liver, the central nervous system,endothelial cells, and muscle. Adenoviruses have the advantage of beingcapable of infecting non-dividing cells. Kozarsky and Wilson, 1993,Current Opinion in Genetics and Development 3:499-503 present a reviewof adenovirus-based gene therapy. Bout et al., 1994, Human Gene Therapy5:3-10 demonstrated the use of adenovirus vectors to transfer genes tothe respiratory epithelia of rhesus monkeys. Other instances of the useof adenoviruses in gene therapy can be found in Rosenfeld et al., 1991,Science 252:431-434; Rosenfeld et al., 1992, Cell 68:143-155; andMastrangeli et al., 1993, J. Clin. Invest. 91:225-234. Adeno-associatedvirus (AAV) has also been proposed for use in gene therapy (Walsh etal., 1993, Proc. Soc. Exp. Biol. Med. 204:289-300.

Alternatively, mesenchymal stem cells which express gap junctionalprotein may be genetically engineered to express the therapeutic nucleicacid of interest followed by transplantation into tumor tissue, i.e,prostate tumor tissue. It has been demonstrated that siRNA, for example,can cross gap junctional channels to affect the function of target cells(Valiunas et al., 2005, J. Physiol. (Lond) 568:459-468).

In another embodiment of the invention, nucleic acid moleculescomprising a sequence encoding a dominant negative mutant TREK-1 proteinor non-functional fragment or derivative thereof, are administered toinhibit TREK-1 function. The TREK-1 channel is normally found in thecell as a homodimer. When a dominant-negative mutant TREK-1 protein isoverexpressed it forms a heterodimer with the endogenous wild-typemonomers resulting in a non-functional channel. Thus, dominant negativeTREK-1 mutants are those mutants that are defective in function buteffective in binding to form heterodimers with the wild type TREK-1.Specifically, the nucleic acid comprises a TREK-1 nucleic acid that ispart of an expression vector that expresses a dominant non-functionalTREK-1 protein or fragment or chimeric protein thereof in cancer cells.In a specific embodiment of the invention, a dominant negative TREK-1can be created by mutating a key residue in the ion selectivity filterin both pore-forming loops (G161E and G268E). Dominant non-functionalTREK-1 can be engineered for expression in cancer cells thatinappropriately overexpress TREK-1.

The present invention is directed to a method of modulating cellproliferation comprising contacting a cell with a composition comprisinga nucleic acid sequence, wherein the nucleotide sequence encodes avariant TREK-1 that has dominant negative activity. In a specificembodiment, the nucleic acid encoding the dominant negative mutantTREK-1 is directly administered in vivo, where it is expressed toproduce the non-functional TREK-1 gene product. This can be accomplishedusing any of the gene therapy methods described above for in vivoexpression of therapeutic nucleic acid molecules.

The form and amount of therapeutic nucleic acid envisioned for usedepends on the cancer, desired effect, patient state, etc., and can bedetermined by one skilled in the art.

Antibodies exhibiting capability to down regulate TREK-1 gene productactivity can also be utilized to treat cancer. Such antibodies can begenerated using standard techniques. Such antibodies include but are notlimited to polyclonal, monoclonal, Fab fragments, single chainantibodies, chimeric antibodies, and the like.

5.4. Pharmaceutical Preparations and Methods of Administration

The compounds and nucleic acid sequences described herein can beadministered to a patient at therapeutically effective doses to treat orprevent cancer. A therapeutically effective dose refers to that amountof a compound sufficient to result in a healthful benefit in the treatedsubject.

Toxicity and therapeutic efficacy of compounds can be determined bystandard pharmaceutical procedures in cell cultures or experimentalanimals, e.g., for determining the LD₅₀ (the dose lethal to 50% of thepopulation) and the ED₅₀ (the dose therapeutically effective in 50% ofthe population). The dose ratio between toxic and therapeutic effects isthe therapeutic index and it can be expressed as the ratio LD₅₀/ED₅₀.Compounds which exhibit large therapeutic indices are preferred. Whilecompounds that exhibit toxic side effects can be used, care should betaken to design a delivery system that targets such compounds to thesite of affected tissue in order to minimize potential damage touninfected cells and, thereby, reduce side effects.

The data obtained from the cell culture assays and animal studies can beused in formulating a range of dosage for use in humans. The dosage ofsuch compounds lies preferably within a range of circulatingconcentrations that include the ED₅₀ with little or no toxicity. Thedosage can vary within this range depending upon the dosage formemployed and the route of administration utilized. For any compound usedin the method of the invention, the therapeutically effective dose canbe estimated initially from cell culture assays. A dose can beformulated in animal models to achieve a circulating plasmaconcentration range that inhibits TREK-1 by 50% as determined in cellculture. Such information can be used to more accurately determineuseful doses in humans. Levels in plasma can be measured, for example,by high performance liquid chromatography.

Pharmaceutical compositions for use in accordance with the presentinvention can be formulated in conventional manner using one or morephysiologically acceptable carriers or excipients. Thus, the compoundsand their physiologically acceptable salts and solvents can beformulated for administration by inhalation or insufflation (eitherthrough the mouth or the nose) or oral, buccal, parenteral or rectaladministration. In a specific embodiment of the invention, thepharmaceutical compositions of the invention may be implanted directlyinto, or in close proximity, to the tumor tissue. For example, thepharmaceutical compositions may be implanted into the prostate, thereby,allowing the administration of higher doses of drug to a more limitedtissue area. Such compositions may be formulated into a form that allowsfor sustained release of the drug in the area to be treated.

For oral administration, the pharmaceutical compositions can take theform of, for example, tablets or capsules prepared by conventional meanswith pharmaceutically acceptable excipients such as binding agents(e.g., pregelatinised maize starch, polyvinylpyrrolidone orhydroxypropyl methylcellulose); fillers (e.g., lactose, microcrystallinecellulose or calcium hydrogen phosphate); lubricants (e.g., magnesiumstearate, talc or silica); disintegrants (e.g., potato starch or sodiumstarch glycolate); or wetting agents (e.g., sodium lauryl sulphate). Thetablets can be coated by methods well known in the art. Liquidpreparations for oral administration can take the form of, for example,solutions, syrups or suspensions, or they can be presented as a dryproduct for constitution with water or other suitable vehicle beforeuse. Such liquid preparations can be prepared by conventional means withpharmaceutically acceptable additives such as suspending agents (e.g.,sorbitol syrup, cellulose derivatives or hydrogenated edible fats);emulsifying agents (e.g., lecithin or acacia); non-aqueous vehicles(e.g., almond oil, oily esters, ethyl alcohol or fractionated vegetableoils); and preservatives (e.g., methyl or propyl-p-hydroxybenzoates orsorbic acid). The preparations can also contain buffer salts, flavoring,coloring and sweetening agents as appropriate.

Preparations for oral administration can be suitably formulated to givecontrolled release of the active compound. For buccal administration thecompositions can take the form of tablets or lozenges formulated inconventional manner.

For administration by inhalation, the compounds for use according to thepresent invention are conveniently delivered in the form of an aerosolspray presentation from pressurized packs or a nebulizer, with the useof a suitable propellant, e.g., dichlorodifluoromethane,trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide orother suitable gas. In the case of a pressurized aerosol the dosage unitcan be determined by providing a valve to deliver a metered amount.Capsules and cartridges of e.g. gelatin for use in an inhaler orinsufflator can be formulated containing a powder mix of the compoundand a suitable powder base such as lactose or starch.

The compounds can be formulated for parenteral administration (i.e.,intravenous or intramuscular) by injection, via, for example, bolusinjection or continuous infusion. Formulations for injection can bepresented in unit dosage form, e.g., in ampoules or in multi-dosecontainers, with an added preservative. The compositions can take suchforms as suspensions, solutions or emulsions in oily or aqueousvehicles, and can contain formulatory agents such as suspending,stabilizing and/or dispersing agents. Alternatively, the activeingredient can be in powder form for constitution with a suitablevehicle, e.g., sterile pyrogen-free water, before use.

The compounds can also be formulated in rectal compositions such assuppositories or retention enemas, e.g., containing conventionalsuppository bases such as cocoa butter or other glycerides.

In addition to the formulations described previously, the compounds canalso be formulated as a depot preparation. Such long acting formulationscan be administered by implantation (for example subcutaneously orintramuscularly) or by intramuscular injection. Thus, for example, thecompounds can be formulated with suitable polymeric or hydrophobicmaterials (for example as an emulsion in an acceptable oil) or ionexchange resins, or as sparingly soluble derivatives, for example, as asparingly soluble salt.

6. EXAMPLE Two-Pore Domain K+ Channels Are Over-Expressed in Cancer

Initial studies of prostate epithelium have identified expression of theTREK-1 two pore channel in two prostate cancer cell lines, PC-3 andLNCaP but not in normal prostate epithelial cells (NPE; FIG. 1).Expression of functional channels in both PC-3 (FIG. 2, Panel A) andLNCaP (data not shown) cells has been confirmed by whole-cellpatch-clamp recording in the voltage-clamp configuration. TREK-1 wasidentified in these recordings as the sipatrigine-sensitive current inthe presence of CsCl (5 mM), TEA (10 mM) and nifedipine (5 μM) whichwere are added to block other K⁺ and the I_(CaL) currents. Normalprostate epithelial cells do not express any TREK-1 current under theseconditions (see FIG. 4, below). In addition, a TREK-1 channel mutant hasbeen created which is disrupted in the selectivity filter of the poreregion (G161E/G268E). This mutant channel carries no current whenexpressed in CHO cells and functions as a dominant-negative (dn-TREK)when co-expressed with wild-type channel. Transfection of PC-3 cellswith do-TREK (FIG. 2, Panel B) leads to complete ablation of endogenousTREK-1 current.

Additional studies have identified the presence of TASK-1 (identified asa methanandamide-sensitive current) (Maingret et al., 2001) and TASK-3(identified as a ruthenium red-sensitive current) (Czirjak and Enyedi,2003) in both LNCaP and PC-3 cells.

Since TREK-1 is expressed in the prostate cancer cells but not in NPE,such data indicates that TREK-1 might contribute to the rapidproliferation rate of prostate cancer cells. To confirm this hypothesis,the proliferation of untransfected PC-3 cells was compared with cellsthat were transfected either with the dominant-negative TREK-1 or anempty vector (pEGFP). The cells which over-express the dn-TREK carry noTREK-1 current (see FIG. 2, Panel B). Proliferation rate was determinedusing a standard colorimetric assay (Cell Proliferation Kit I [MTT];Roche) and normalized to the proliferation rate of untransfected PC-3.pEGFP transfection does not affect the proliferation rate of PC-3 cells.However, over-expression of dn-TREK significantly slows theproliferation rate by 44±6.6% (FIG. 3; n=6). It should be noted that thetransfection efficiency in these experiments is approximately 30%. Whilethis is not an issue for the electrophysiology experiments where cellsexpressing the dominant-negative channel can be individually selecteddue to the co-expression of EGFP, the efficiency should be expected toreduce the effect observed in the proliferation assay which measures therate of all the cells in the microplate. Therefore, the 47% inhibitionis believed to be an underestimate of the effect.

To test whether over-expression of TREK-1 in normal prostate epithelialcells would increase the proliferative rate experiments were conductedwith a TREK-1 bearing adenovirus. Normal prostate epithelial cells donot exhibit TREK-1 current (FIG. 4, Panel A). However, when NPE areinfected with the TREK-1 virus a large current is readily detected (FIG.4, Panel B). The effect of this current on the proliferation rate in NPEwas tested and it was determined that expression of TREK-1 significantlyincreased the proliferation rate of NPE by 270±27.7% (FIG. 5, n=5,p<0.05).

As demonstrated in FIG. 5, expression of TREK-1 increases proliferationof normal prostate epithelial cells (NPE). Normal prostate epithelialcell cultures were obtained from Clonetics and infected with aTREK-1-containing adenovirus. Some virally infected cells were alsotreated with sipatrigine (10 μM), a TREK-1 blocker. Cell proliferationwas assessed using the MTT assay as described in FIG. 3. These data arepresented as mean±SEM from five paired experiments. * p<0.05, theNPE/TREK-1 group differed significantly from each of the othertreatments and no other groups were different.

FIG. 6 demonstrates, by immunohistochemical staining of human prostatetissue, that TREK-1 is over-expressed in cancer. Human tissue sampleswere stained with rabbit polyclonal anti-human TREK-1 antibody(Alomone). Panels A and B show a low power and high power view of thesame field. Under the low power, a normal gland is visible (centerright). The epithelial cells lining the luminal surface are very lightlystained. An adjacent cancerous gland (center left) shows a very smallluminal space and the epithelial cells lining it are very denselystained indicating an overexpression of TREK-1. The same features arevisible under higher power in Panel B.

FIG. 7 reveals that Meclofenamate activates TREK-1 current in CHO cellsthat heterologously express the channel. CHO cells were transfected witha plasmid encoding human TREK-1 and the current was studied by patchclamp. The current-voltage relation was determined using a ramp protocolthat went from −130 mV to +40 mV in 6 s (after correction for thejunction potential). Current was greater in the presence ofmeclofenamate. This is typical of 7 cells.

Further, FIG. 8 reveals that Trifluoperazine inhibits TREK-1 current inCHO cells that heterologously express the channel. CHO cells weretransfected with a plasmid encoding human TREK-1 and the current wasstudied by patch clamp. The current-voltage relation was determinedusing a ramp protocol that went from −130 mV to +40 mV in 6 s (aftercorrection for the junction potential). Current was less in the presenceof trifluoperazine. This is typical of 3 cells.

Transiently transfected CHO cells (obtained through ATCC) were fixedwith 1 ml ice-cold 70% ethanol 48 h after transfection with TREK-1.Fixation was followed by RNase treatment and staining with propidiumiodide (50 μg/ml). Stained samples were analyzed on a FACScan flowcytometer and data were analyzed using Cell Quest software to assess thecell-cycle distribution patterns. FIGS. 10-12 demonstrate that TREK-1CHO stable over-expressor cell lines have significantly higherproliferation rates which correlate with the TREK-1 current.

Anchorage-independent growth of stably transfected CHO cells was alsomeasured. Creation of the TREK-1 stable over-expressing lines was donein CHO cells using zeocin selection. CHO cells that stablyover-expressed TREK-1 (1×10⁶ cells/well) were suspended in 0.4% agarwith complete RPMI medium in six well plates. Twenty days later theplates were stained with iodonitrotetrazolium chloride for 6 h. Colonieswere scored using a light microscope at ×10 magnification. Asdemonstrated in FIG. 13, TREK-1 over-expression promotesanchorage-independent growth.

The present invention is not to be limited in scope by the specificembodiments described herein which are intended as single illustrationsof individual aspects of the invention, and functionally equivalentmethods and components are within the scope of the invention. Indeed,various modifications of the invention, in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such modificationsare intended to fall within the scope of the claims. Throughout thisapplication various publications are referenced. The disclosures ofthese publications in the entireties are hereby incorporated byreference into this application in order to more fully describe thestate of the art to those skilled therein as of the date of theinvention described and claimed herein.

1. A method for identifying a compound that activates TREK-1 activitycomprising (i) contacting a cell expressing TREK-1 with a test compoundand measuring the level of TREK-1 activity; (ii) in a separateexperiment, contacting a cell expressing TREK-1 protein with a vehiclecontrol and measuring the level of TREK-1 activity where the conditionsare essentially the same as in part (i), and then (iii) comparing thelevel of TREK-1 activity measured in part (i) with the level of TREK-1activity measured in part (ii), wherein an increased level of TREK-1activity measured in part (i) compared to the level measured in part(ii) indicates that the test compound is a TREK-1 activator.
 2. A methodfor identifying a compound that inhibits TREK-1 activity comprising (i)contacting a cell expressing TREK-1 protein with a test compound andmeasuring the level of TREK-1 activity, (ii) in a separate experiment,contacting a cell expressing TREK-1 protein with a vehicle control andmeasuring the level of TREK-1 activity, where the conditions areessentially the same as in part (i) and then (iii) comparing the levelof TREK-1 activity measured in part (i) with the level of TREK-1activity measured in part (ii), wherein a decreased level of TREK-1activity in part (i) compared to the level measured in part (ii)indicates that the test compound is a TREK-1 inhibitor.
 3. A method foridentifying a compound that inhibits proliferation of cells expressingTREK-1 activity comprising (i) contacting a cell expressing TREK-1protein with a test compound and measuring the level of cellproliferation, (ii) in a separate experiment, contacting a cellexpressing TREK-1 protein with a vehicle control and measuring the levelof cell proliferation, where the conditions are essentially the same asin part (i) and then (iii) comparing the level of cell proliferationmeasured in part (i) with the level of cell proliferation measured inpart (ii), wherein a decreased level of cell proliferation measured inpart (i) compared to the level measured in part (ii) indicates that thetest compound is an inhibitor of cell proliferation.
 4. A method fordiagnosis and/or prognosis of cancer in a subject comprising: (a)detecting the level of TREK-1 expression in a sample derived from asubject; and (b) comparing the level of TREK-1 expression detected inthe subject's sample to the level of TREK-1 expression detected in acontrol sample, wherein an increase in the level of TREK-1 expressiondetected in the subject's sample as compared to a control sample is anindicator of a subject with cancer or progression toward cancer.
 5. Themethod of claim 1 wherein the level of TREK-1 RNA expression ismeasured.
 6. The method of claim 1 wherein the level of TREK-1 proteinexpression is measured.
 7. The method of claim 3 wherein the level ofTREK-1 protein expression is measured using an immunoassay.
 8. Themethod of claim 1 wherein an increase in the level of TREK-1 expressiondetected in the subject's sample as compared to a control sample is anindicator of a subject with cancer or progression toward cancer.
 9. Amethod for monitoring the therapeutic effect of a cancer treatment on asubject comprising: measuring at time intervals before, during, or aftercancer treatment the amount of a TREK-1 expression wherein a change orabsence of change in the amount of the TREK-1 gene expression iscorrelated with the effect of the cancer treatment on the subject. 10.The method of claim 5 wherein a decrease in the level of TREK-1expression during or after cancer treatment as compared to the level ofTREK-1 expression before treatment is correlated with a positiveresponse to the treatment.
 11. The method of claim 6 wherein the levelof TREK-1 RNA expression is measured.
 12. The method of claim 6 whereinthe level of TREK-1 protein expression is measured
 13. The method ofclaim 9 wherein the level of TREK-1 protein expression is measured usingan immunoassay.